In various countries there are private vans that ride along the normal bus routes, marked with the same numbers as the buses. They work exactly like buses, collecting and leaving people at the stops, but they're much smaller and usually more frequent. I always thought they were an excellent solution- I don't get why there shouldn't be anything in between big, rare, and shared public buses and small, on-demand, individual private cars.
See: Маршрутка (Marshrutka), Colectivo, Matatu
I'm not really aware of many rich countries that operate minibusses in urban areas. The bulk of the cost of operating public transport is labor so there's a strong incentive to scale.
Now if we get Waymo style self driving minibusses, that'd be great. But if the running costs for full size electric busses aren't too dissimilar it might just make sense to standardize on larger automated busses for increased surge capacity.